A variable displacement pump includes: a first pressure control chamber; a second pressure control chamber; a spring arranged to urge the cam ring in a second swing direction; a hydraulic pressure supply valve arranged to be opened by a predetermined hydraulic pressure, and thereby to introduce a control hydraulic pressure to the first control chamber; a connection passage formed in the housing or the cam ring, and arranged to connect the first pressure control chamber and the second pressure control chamber; and a relief circuit arranged to connect the second pressure control chamber and a low pressure side, to be opened or closed in accordance with a swing position of the cam ring, and to be closed when the cam ring is swung by a predetermined amount in the first direction.

A variable displacement pump includes: a first pressure control chamber; a second pressure control chamber; a spring arranged to urge the cam ring in a second swing direction; a hydraulic pressure supply valve arranged to be opened by a predetermined hydraulic pressure, and thereby to introduce a control hydraulic pressure to the first control chamber; a connection passage formed in the housing or the cam ring, and arranged to connect the first pressure control chamber and the second pressure control chamber; and a relief circuit arranged to connect the second pressure control chamber and a low pressure side, to be opened or closed in accordance with a swing position of the cam ring, and to be closed when the cam ring is swung by a predetermined amount in the first direction.

A rotary fluid drive has first and second bodies 20, 120. The second body 120 is rotatable relative to and inside of the first body 20 defining a working fluid space 40 there between. Gates 130 are supported by the first body 20 and lobes 124 are provide on the second body 120. Gate pockets 26 are formed in the first body 20 into which the gates swing when contacted by the lobes 124. The gates 130 and the gate pockets 26 are configured to form a debris chamber 27 there between capable of temporarily accommodating solid debris. Each gate 130 has a plurality of projections 136A with intervening gaps 136B. The gaps form a gate pocket flow path 141. Working fluid flows via each gate pocket flow path 141 into the working fluid space 40 when the associated gate 130 is maximally deflected into its associated gate pocket 26.